Mechanistic Dichotomy in Bacterial Trichloroethene Dechlorination Revealed by Carbon and Chlorine Isotope Effects
Mechanistic Dichotomy in Bacterial Trichloroethene Dechlorination Revealed by Carbon and Chlorine Isotope Effects
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DOI：
10.1021/acs.est.8b06643
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发表时间：
2019-04-16
影响因子：
11.4
通讯作者：
Elsner, Martin
中科院分区：
文献类型：
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作者：
Lihl, Christina;Douglas, Lisa M.;Elsner, Martin
四氯乙烯和三氯乙烯是地下水中重要的污染物。在污染地点的微生物还原脱卤可以产生无毒的乙烯，但通常停止于有毒的顺-1,2-二氯乙烯（顺- dce）或氯乙烯（VC）。碳相对于氯同位素效应的大小（用Lambda（C/Cl）表示，δ C-13与δ Cl-37回归的斜率）最近被认为揭示了维生素B-12作为还原脱卤酶活性的模型反应物的不同还原机制。顺式dce的较大Lambda（C/Cl）值反映了cob(I)alamin添加后的质子化，而PCE的较小Lambda（C/Cl）值表明cob(I)alamin添加后的Cl-消除。本研究解决了实际微生物的脱卤问题，并观察到顺式dce的Lambda（C/Cl）值相同大（Lambda(C/Cl) = 10.0至17.8），而TCE和PCE的Lambda（C/Cl）值相同小（Lambda(C/Cl) = 2.3至3.8）。对于TCE，混合培养在VC或dce上预培养，然后再面对TCE (Lambda(C/Cl) = 9.0 ~ 18.2)，甚至可以扭转小Lambda（C/Cl）的趋势。这一观察结果提供了明确的证据，表明底物适应必须选择具有不同机制基序的还原脱卤酶。Lambda（C/Cl）的模式几乎与迄今为止发表的所有研究一致，而反应机制的差异为长期存在的问题提供了一个潜在的答案，即为什么生物修复经常在cis-DCE停止。
Tetrachloroethene (PCE) and trichloroethene (TCE) are significant groundwater contaminants. Microbial reductive dehalogenation at contaminated sites can produce nontoxic ethene but often stops at toxic cis-1,2-dichloroethene (cis-DCE) or vinyl chloride (VC). The magnitude of carbon relative to chlorine isotope effects (as expressed by Lambda(C/Cl), the slope of delta C-13 versus delta Cl-37 regressions) was recently recognized to reveal different reduction mechanisms with vitamin B-12 as a model reactant for reductive dehalogenase activity. Large Lambda(C/Cl) values for cis-DCE reflected cob(I)alamin addition followed by protonation, whereas smaller Lambda(C/Cl) values for PCE evidenced cob(I)alamin addition followed by Cl- elimination. This study addressed dehalogenation in actual microorganisms and observed identical large Lambda(C/Cl) values for cis-DCE (Lambda(C/Cl) = 10.0 to 17.8) that contrasted with identical smaller Lambda(C/Cl) for TCE and PCE (Lambda(C/Cl) = 2.3 to 3.8). For TCE, the trend of small Lambda(C/Cl) could even be reversed when mixed cultures were precultivated on VC or DCEs and subsequently confronted with TCE (Lambda(C/Cl) = 9.0 to 18.2). This observation provides explicit evidence that substrate adaptation must have selected for reductive dehalogenases with different mechanistic motifs. The patterns of Lambda(C/Cl) are consistent with practically all studies published to date, while the difference in reaction mechanisms offers a potential answer to the long-standing question of why bioremediation frequently stalls at cis-DCE.